Metal-oxide-semiconductor capacitor based passive amplifier
A passive amplifier is provided that includes an input sampling switch, a sampling capacitance, and metal-oxide-semiconductor capacitor devices. An input signal may be sampled onto the sampling capacitance by turning on the input sampling switch while the metal-oxide-semiconductor capacitors are activated. After the sampling phase, the metal-oxide-semiconductor capacitors are deactivated to provide a voltage gain. The voltage gain can be conditionally applied depending on the signal level of the sampled input.
1. An image sensor, comprising:
an image sensor pixel;
a column line configured to receive a signal from the image sensor pixel; and
a passive amplifier circuit comprising:
an input port configured to receive the signal from the column line;
an output port;
a sampling switch having a first terminal coupled to the input port and having a second terminal coupled to the output port; and
a metal-oxide-semiconductor capacitor having a gate terminal configured to receive a control signal and having source-drain terminals coupled to the output port.
2. The image sensor of claim 1 , wherein the passive amplifier circuit further comprises:
a capacitor having a first terminal coupled to the output port and having a second terminal configured to receive a reference voltage; and
an additional metal-oxide semiconductor capacitor having a gate terminal configured to receive an inverted version of the control signal and having source-drain terminals coupled to the output port.
3. The image sensor of claim 2 , wherein the metal-oxide-semiconductor capacitor comprises an n-type metal-oxide-semiconductor capacitor and wherein the additional metal-oxide-semiconductor capacitor comprises a p-type metal-oxide-semiconductor capacitor.
4. The image sensor of claim 2 , wherein the metal-oxide-semiconductor capacitor and the additional metal-oxide-semiconductor capacitor are activated during a charge sampling phase and are deactivated during an amplification phase.
5. The image sensor of claim 4 , wherein the reference voltage has a given voltage level during the charge sampling phase and has the given voltage level during the amplification phase.
6. The image sensor of claim 4 , wherein the reference voltage has a first voltage level during the charge sampling phase and has a second voltage level, different than the first voltage level, during the amplification phase.
7. The image sensor of claim 2 , wherein the passive amplifier circuit further comprising:
a comparator having an input coupled to the first terminal of the capacitor and an output on which the control signal is generated.
8. The image sensor of claim 7 , wherein the comparator is configured to deassert the control signal when the signal at the input port is within a predetermined voltage range.
9. An amplifier, comprising:
an input port;
an output port;
a sampling switch having a first terminal coupled to the input port and having a second terminal coupled to the output port; and
a metal-oxide-semiconductor capacitor having source-drain terminals coupled to the output port and having a gate terminal configured to receive a control signal.
10. The amplifier of claim 9 , further comprising:
an additional metal-oxide-semiconductor capacitor having source-drain terminals coupled to the output port and having a gate terminal configured to receive an inverted version of the control signal.
11. The amplifier of claim 10 , further comprising:
a capacitor having a first terminal coupled to the output port and having a second terminal configured to receive a reference voltage.
12. The amplifier of claim 11 , wherein:
the control signal is driven high during a charge sampling operation;
the control signal is driven low during an amplification operation;
the reference voltage has a first voltage level during the charge sampling operation; and
the reference voltage has the first voltage level or a second voltage level, different than the first voltage level, during the amplification operation.
13. The amplifier of claim 11 , wherein:
the control signal is driven high during a sampling operation; and
the control signal is driven low during an amplification operation.
14. The amplifier of claim 11 , wherein:
the reference voltage has a first voltage level during the sampling operation; and
the reference voltage has the first voltage level or a second voltage level, different than the first voltage level, during the amplification operation.
15. The amplifier of claim 10 , wherein the metal-oxide-semiconductor capacitor comprises an n-type metal-oxide-semiconductor capacitor and wherein the additional metal-oxide-semiconductor capacitor comprises a p-type metal-oxide-semiconductor capacitor.
16. The amplifier of claim 10 , wherein the metal-oxide-semiconductor capacitor and the additional metal-oxide-semiconductor capacitor are activated during a first phase and are deactivated during a second phase different than the first phase.
17. The amplifier of claim 16 , wherein the first phase comprises a sampling phase and wherein the second phase comprises an amplification phase.
18. The amplifier of claim 9 , further comprising:
a comparator having an input coupled to the second terminal of the sampling switch and an output at which the control signal is produced.
19. The amplifier of claim 18 , wherein the comparator is configured to deassert the control signal when a signal at the input port is within a predetermined voltage range.
20. The amplifier of claim 18 , further comprising:
an inverter having an input coupled to the output of the comparator and to the gate terminal of the metal-oxide-semiconductor capacitor.